1. Field of the Invention
The present invention pertains to thermal ink jet printheads and more particularly to the thermal ink jet chip architecture for transducers and transistors formed on the surface of the thermal ink jet chip. More specifically, the present invention relates to a thermal ink jet (TIJ) resistor element which is formed on top of a silicon dioxide field oxide layer and a secondary printhead heating resistor which is formed from an n.sup.- diffusion in the silicon substrate under the field oxide. By placing the secondary diffused resistor in the substrate and under the TIJ resistor elements, a compact thermal ink jet chip can be designed and the n- resistor elements are able to rapidly heat the printhead drop ejection region. Close temperature control of the drop ejection region enables uniform ink droplet volume to be ejected.
2. Description of the Related Art
Thermal ink jet marking technology has resulted in low cost monochrome and process color printing. Because the size of the ejected ink droplet (and resultant printed pixel) is sensitive to the transducer temperature, it is important to achieve good temperature control. Temperature control is most easily achieved by selecting an operating point above ambient, typically around 35.degree.-45.degree. C. Problems which are encountered with elevated operating temperature include degasing of ink due to decreased gas solubility which can lead to air bubble generation; extended warm-up time before the first print can be made; and possible reliability problems resulting from the transducer being exposed to elevated temperatures for an extended length of time.
U.S. Pat. No. 4,539,571 to Suzuki discloses a thermal printing system wherein an auxiliary resistor is shown which keeps a printhead warm. U.S. Pat. No. 4,429,321 to Matsumoto discloses a liquid jet recording head wherein an electrothermal transducer and its driver are formed upon a single substrate. U.S. Pat. No. 4,769,527 to Hart et al discloses a thermal image generating device wherein a pair of resistors are used to create a more uniform image.
U.S. Pat. No. 4,623,903 to Hashimoto discloses a thermal printhead having two resistors, a main heater resistor and an auxiliary resistor for maintaining constant temperature of the thermal head. U.S. Pat. No. 4,472,875 to Christian et al discloses a method for manufacturing an integrated circuit device by forming a transducer and a driver circuit for a thermal printhead on a single substrate. U.S. Pat. No. 4,719,477 to Hess discloses an integrated thermal ink jet printhead and method of manufacture which utilizes an on-chip MOSFET driver.
As further background, U.S. Pat. Nos. 4,774,530 (Ink Jet Printhead) and 4,532,530 (Bubble Jet Printing Device) to Hawkins are hereby incorporated by reference for their disclosures of the structure and operation of thermal ink jet printheads.
However, a need still exists for a thermal ink jet printing chip which incorporates an architectural design which could be easily incorporated into typical chip fabricating processes and which would allow rapid heating of the transducer element and high voltage operation of the driver elements with the driver and transducer both being located upon the same chip.